Publication: Estudio de máquinas de absorción con la disolución nitrato de litio-amoniaco : ciclos híbridos potenciados con compresión mecánica
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2010-06
Defense date
2010-07-16
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Abstract
En esta Tesis doctoral se lleva a cabo un estudio de máquinas de absorción para refrigeración que sean capaces de funcionar con menores temperaturas de generación que los ciclos basados en simple efecto. Esto permitiría aprovechar calores residuales y calor solar a menor temperatura con la consiguiente reducción de emisiones de CO2. Los ciclos híbridos de absorción basados en simple efecto, potenciados con compresión mecánica, ofrecen esta posibilidad además de permitir una modulación en potencia de interés. Para la evaluación de estos ciclos híbridos se realiza un modelo numérico que incluye cambio de fase en los cambiadores de calor. Con él se determina cuánto disminuye la temperatura de generación con respecto al ciclo de simple efecto y se estudian en profundidad los cambios en los procesos, el comportamiento y rendimientos del propio ciclo. Por último se analiza su interés medioambiental. Además del estudio teórico, se realiza un estudio experimental del ciclo híbrido utilizando tecnologías que permiten la reducción del tamaño de las máquinas de absorción, como absorbedores adiabáticos con fase dispersa (en forma de gotas) e intercambiadores de placas. Mediante los resultados experimentales se evalúa el funcionamiento del compresor termoquímico como parte del ciclo híbrido. Se realiza una comparación con los resultados obtenidos mediante la simulación, encontrando un elevado grado de concordancia. También se analiza como varía la absorción adiabática mediante gotas y la ebullición en intercambiadores de placas en los diferentes puntos de trabajo del ciclo híbrido. En concreto se estudia como varían esos procesos con el cambio de concentración de la disolución, la cual ha sido NH3-LiNO3, cuyas propiedades le confieren ser un sustituto del NH3-H2O. Por último se analiza, mediante un modelo numérico, como afectan la recirculación y el factor de aproximación al equilibrio adiabático en el absorbedor a los ciclos de absorción, eventualmente potenciados con compresión mecánica y con absorbedor adiabático. Mediante el modelo se determina la recirculación óptima y se compara los resultados con ciclos con absorbedores no adiabáticos, evaluando las ventajas y desventajas de la absorción adiabática.------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This doctoral Thesis develops a study on absorption machines for refrigeration capable of working at lower driving temperatures than the single-effect absorption cycles. This would make possible the use of residual heat and solar heat at lower temperatures, reducing the CO2 emissions. The single-3effect absorption cycles hybridized and integrated with a compression booster offer this possibility, at the same time offering an interesting modulation capability of the refrigerating capacity. A numerical model has been developed to evaluate the performance of these hybrid cycles, including phase change in the heat exchangers. It allows determining the decrease in driving temperature of these cycles in comparison with the basic singleeffect alternative. Besides that, the model allows deepening in the study of the processes, performance and efficiency of the cycles. Finally, an environmental impact analysis is carried out. In addition to the theoretical analysis, an experimental study is performed using technologies that permit reducing the size of the machine, such as: adiabatic dispersed phase (such as drops) absorbers and plate heat exchangers. The behaviour of the thermochemical compressor as part of the hybrid cycle is studied by means of the experimental results. The model results are compared with the experimental results, finding a good agreement. Adiabatic absorption by droplets and boiling heat transfer inside plate heat exchangers are analysed for the different hybrid cycle operating points. Specifically these processes are studied when the solution concentration is changed. The working fluid studied is a solution of NH3-LiNO3, which seems to be a candidate to replace NH3-H2O. Finally, the recirculation and the adiabatic approach to equilibrium factor in adiabatic absorbers are studied by means of a numerical model in absorption cycles integrated with compression booster. The model allows determining the optimum solution recirculation ratio and the results are compared with the non-adiabatic cycle performances, evaluating the advantages and disadvantages of the adiabatic absorption.
This doctoral Thesis develops a study on absorption machines for refrigeration capable of working at lower driving temperatures than the single-effect absorption cycles. This would make possible the use of residual heat and solar heat at lower temperatures, reducing the CO2 emissions. The single-3effect absorption cycles hybridized and integrated with a compression booster offer this possibility, at the same time offering an interesting modulation capability of the refrigerating capacity. A numerical model has been developed to evaluate the performance of these hybrid cycles, including phase change in the heat exchangers. It allows determining the decrease in driving temperature of these cycles in comparison with the basic singleeffect alternative. Besides that, the model allows deepening in the study of the processes, performance and efficiency of the cycles. Finally, an environmental impact analysis is carried out. In addition to the theoretical analysis, an experimental study is performed using technologies that permit reducing the size of the machine, such as: adiabatic dispersed phase (such as drops) absorbers and plate heat exchangers. The behaviour of the thermochemical compressor as part of the hybrid cycle is studied by means of the experimental results. The model results are compared with the experimental results, finding a good agreement. Adiabatic absorption by droplets and boiling heat transfer inside plate heat exchangers are analysed for the different hybrid cycle operating points. Specifically these processes are studied when the solution concentration is changed. The working fluid studied is a solution of NH3-LiNO3, which seems to be a candidate to replace NH3-H2O. Finally, the recirculation and the adiabatic approach to equilibrium factor in adiabatic absorbers are studied by means of a numerical model in absorption cycles integrated with compression booster. The model allows determining the optimum solution recirculation ratio and the results are compared with the non-adiabatic cycle performances, evaluating the advantages and disadvantages of the adiabatic absorption.
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Refrigeración, Máquinas de absorción, Ciclos híbridos